Azure MFA "Activation Failed" error with Microsoft Authenticator App

I already posted a separate reply, but in the time since...  I may have found a solution.  I don't like coming across posts without something to try, so wanted to add my steps here (you never know when someone else is looking for it).  Again though (here comes the disclaimer), this is an old post (no further info from the original case, so it could be that we're dealing with 2 different issues).  Whilst my error message matched exactly that shared in the original post, from the research I did it looks like there may be other error messages that could be the same/similar issue (and don't mention 'push notifications' in the error).

To be clear, we were seeing this error for one user at the point of scanning a QR code in the Microsoft Authenticator app to add an account (Office 365 account where we had just enabled the user's MFA).

First, probably worth sharing the first few basic things we tried;

- Try again

- Try manually with code and URL

- Try configuring MFA through an incognito/private window

- Check device push notifications

- Check device permissions

- Check device for latest OS and app updates

- Deleted and reinstalled the MS Authenticator app

- Disable and re-enable user's MFA (requires admin)

I found a link in a separate Microsoft Support article (which may still be useful...  https://support.microsoft.com/en-gb/help/3120908/activation-failed-error-when-you-try-to-set-up-azure-multi-factor-auth).  Link within the article didn't work for me, but am assuming that could be our Azure subscription or the age of the link (article is 2016).

Essentially, we're trying to check if the user's MFA has been blocked.

Whilst the link contained within the above article did not work, this did (as a global admin);

- Go to Azure portal

- Go to Azure Active Directory

- Go to MFA

- Go to Block/unblock users

My problem user was listed there.

- Press Unblock

- Provide Reason

- Press OK

All that remains now is to know why they got blocked in the first place (parking that for a rainy day...  or someone else)